It is known, for example from U.K. Pat. Nos. 1,040,535, 1,399,906 and 1,409,426 to form strips of clips of this general type and from this material.
In U.K. Pat. No. 1,040,535 material was removed from between adjacent clips in a strip so that the clips were left attached to each other by narrow frangible webs. These clips were intended to be applied to bags by apparatus of the type disclosed for example in U.K. Pat. No. 1,013,320.
Formation of the strips in this manner involves loss of material at the portions which are removed from between adjacent clips and the manner of separation of one clip from the next, which was a lateral displacement so as to break the webs at each of their ends, involves the production of stray chips of plastics (i.e. the severed webs) which can contaminate the food or other product within the bag if they should get within it, or can cause malfunction of the clip attaching mechanism. If the webs do not break in the intended fashion they can remain projecting from the edges of the clip to scratch or snag other products or hands of the users or purchasers of the bag.
Apart from the desire to avoid loss of material there are the secondary disadvantages of the presence of elongate webs (or projections) between adjacent clips. One is that if a given surface area is desired in the finished clip the starting length of the clip will be greater to allow for the wastage; thus its linear speed of progression through the manufacturing process will be higher for an eventual given output of clips per unit time. This in turn imposes an added production difficulty on ensuring accuracy in positioning, especially when punching out the aperture. Also, stretching of these elongate webs or projections before use is harmful if (as in existing machines) registration of the clip actually being filled by a bag mouth is obtained with reference to the position of a clip removed in the same strip.
The method of forming a strip of clips disclosed in U.K. Pat. No. 1,399,906 did eliminate the problem of wastage of material since a line of definition was formed, substantially without loss of material, by moving a flap of material out of the plane of material, each end of the flap defining projections extending from one clip into the next. This movement distorted the material of the strip about a lateral axis. This method of forming the line of definition involved longitudinal apparent contraction of a portion of the clip, considered in plan view, had to be carried out with great accuracy in order that the projections should be of the calculated length, and required a distinct planishing operation to restore the flap to the plane of the remainder of the strip. The clips produced still had the disadvantage the projections into the clips tended to separate from them when the clip was attached to a bag neck and removed from the strip and there was still therefore the difficulty of leaving these plastics material chips which could contaminate food or other products or of having projections projecting from the clips so as to scratch or snag the products or people. Also the flaps which form the projections, unless completely and accurately restored into the plane of the strip would tend to bias the strip into a curve and would prevent compactness in a roll of such strip.
The problem therefore remains of providing a strip of clips of this general nature which is formed without substantial loss of material in the separation of one clip from the next without the need for a distinct planishing operation, and at the same time without leaving any possibility of protrusion out of the plane of the strip or of the presence of stray chips of material resulting from separation of joining webs or projections between clips. Furthermore, the problem is also faced of the finding of a method of forming such a clip without loss of material but at the same time without involving the material in the longitudinal apparent contraction which is essential in the process of U.K. Pat. No. 1,399,906 clips and which necessarily also involves the separate planishing operation which must be completely successful unless the strips are to have ledges protruding which prevent compactness in a roll.
The process of manufacture should also not be over-sensitive to variations in the quality of the material operated on and should avoid as far as possible the accumulation of debris in the tool, which latter can lead to inaccuracies (such as lack of planarity discussed above).
Problems also exist in the efficient design of the neck or passage through which the bag has to pass when it is being urged into its condition of retention by the clip, especially from the point of view of ensuring as far as possible a smooth and snag-free progress of the bag mouth into the aperture.